Reconstruction of Magma Flow in Permo–Triassic Intrusions of the Angara–Taseeva Syneclise (Siberian Platform) Based on Magnetic Susceptibility Anisotropy Data

Abstract

Abstract —Based on detailed studies of the anisotropy of magnetic susceptibility (AMS), the directions of magmatic-melt propagation have been reconstructed in large dolerite sills of the Angara–Taseeva syneclise. Half the sites studied showed a magnetic fabric of “normal” type, i.e., the minimum K3 axis of the AMS ellipsoid is orthogonal to the contact, and the other two axes lie in the plane of the intrusive body. Interpreting the orientation of the maximum K1 axis as the direction of the melt flow at such sites, we compiled a scheme of the main magma flow directions. The obtained results are generally consistent with the hypothesis of magma-feeding zone in the central, most downwarped part of the Angara–Taseeva depression. The distribution of the maximum axes of the AMS ellipsoid is different in sills and points to the existence of local intrusion centers. Intrusions with an AMS ellipsoid of “reverse” type are predominant on the periphery of the depression. The sites with a “normal” magnetic fabric do not demonstrate any prevailing direction of magma propagation, because there is no general direction of the melt flow in the peripheral subsurface zones of large intrusions.